This invention relates to high speed food processing machines in which a vertical drive shaft supports and drives food processing blades within an upwardly open food containing bowl. The bowl, which is closed by a lid during food processing, is pivoted for pouring its contents. Typically, a powerful motor on the bottom of the bowl rotates the drive shaft, and a mixing baffle blade is supported through the lid for rotation along and around the inside surface of the bowl for removing and returning foodstuffs from the side of the bowl to the vicinity of the food processing blades for further processing. The blades are removable and interchangeable, so that the blade or other tool configurations may be matched to the processing needs at hand. Machines of this type are highly effective in processing foods, and are so fast (many operations being performed in less than a minute), that the actual processing time is but a small part of the total "turn around" time. That is, it usually takes longer to load and unload the machine than to process the food once it is in the machine.
The interchangeable blades are commonly retained on the drive shaft by a nut which is threaded onto the upper end of the drive shaft after the blades have been positioned thereon. Threading the nut on and off is a time consuming operation and presents certain safety hazards. Instances are known, for example, in which the drive motor was inadvertently connected in reverse, and the blade securing nut was not tight on the drive shaft. When the motor was turned on it ran backwards, the nut was spun off, and as it unthreaded, it acted like a jack screw against the lid and was driven right through the lid of the food processing machine. A need thus remains for a convenient, quick-acting device for securing and releasing the food processing blades on the drive shaft, which will not pose a hazard if it is loose, and which will preferably be indifferent to the direction in which it is operated.